NFL training camps: Guardian Cap players are wearing over helmets, why
The story behind those soft-shell puffy Guardian Caps players have been wearing
Athletic Vols Hit Practice Field For First Time This Preseason - University of Tennessee Athletics
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Puffy Guardian Caps Could Reduce NFL Player Concussions
Guardian Caps Guardian Sports
Why Alabama football players are wearing padded helmets in practice
Steelers Debut New Guardian Caps For Practice As Part Of New NFL Mandate - Steelers Depot
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
Get A Load Of These Big Dumb Helmet Helmets